We will study virus-host cell interactions with respect to i) the effect of vesicular stomatitis virus (VSV) transcription products on host macromolecular functions and ii) the effect of infected cell factors on in vitro viral transcription and replication. We will determine the content of viral transcripts in the nucleus and cytoplasm of acutely and persistently infected cells with particular interest in the role of the leader RNA in the inhibition of host cell transcription. We will determine whether the rapid accumulation of VSV transcripts in the nucleus is the result of viral transcription in the nucleus or selective transport to the nucleus. In addition, nuclear leader RNA will be examined for interactions with proteins that are involved in host or viral RNA synthesis. We will determine whether rabies virus synthesizes a leader RNA in vivo, determine the rabies leader sequence and study its intracellular localization. Therefore, these studies are directed towards understanding the molecular basis of nuclear involvement in rhabdovirus cytopathogenicity. We will study the role of short VSV transcription products in messenger RNA synthesis and the molecular switch to RNA replication. Short capped RNA species sythesized in vitro will be studied in pulse-chase experiments to determine whether they are precursors to mRNA. We will further examine the effects of infected cell extracts on the synthesis of short capped and 5' triphosphated small RNAs. We will biochemically fractionate VSV infected cells and isolate factors that promote the synthesis of polycistronic mRNA and the readthrough of DI particle transcription stop signals. We will determine whether the switch to replicative plus strand synthesis involves chemical modification of the transcriptase, the nucleocapsid template or the RNA product. These studies are, thus, directed towards the development of an in vitro replication system for VSV and an understanding of the molecular basis of VSV gene expression.